Color proofing method and apparatus, and recorded medium on which color proofing program is recorded

ABSTRACT

In a method for improving the color reproducibility of printed matter to be produced by a printing press in proof print produced by a proof press, a look-up table containing converted values of image data over the entire color space with respect to the proof press is created, the look-up table is corrected based on the color of a printing paper for the printing press and a paper exposed area factor in the proofing, and proof print is created by the use of the corrected look-up table. Furthermore, proof printing image data, in which each of levels of monochromatic color gradation of black on the printed matter is represented on the proof print, out of the proof printing image data over the entire color space in a subtractive process resulting from color matching between proof print by the proof press and the printed matter by means of the printing press is corrected in such a manner that a part having a black ink area factor of 100% on the printed matter is represented only with black ink also on the proof print, but that a part other than the part having a black ink area factor of 100% on the printed matter is represented on the proof print by using under color removal, so that the representing characteristics of the black ink on the printed matter are reproduced on the proof print.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from PCT/JP99/03886.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a color proofing method and apparatusfor improving the color reproducibility of printed matter to be producedby a printing press in proof print produced by a proof press in aprinting process.

BACKGROUND ART

Color correction is conducted prior to printing performed by a printingpress. The color correction is conducted in order to check finish ofprinting, for example, 1) the presence or absence of a typographicalerror or gap, 2) the presence or absence of dust, a flaw, a smear or thelike, 3) gradation reproducibility such as brightness or darkness ofprinted matter, 4) the color reproducibility of the printed matter, 5)the sharpness of the printed matter, and the like.

The color correction is generally conducted on the basis of proofprinting performed by a proof press. In particular, computerization ofpre-printing processing has been progressed in recent years, andtherefore, there has been prevailed a digital proof press which canproduce proof print directly based on digital data by means of an inkjet system or a sublimation thermal ink-transfer system.

In this case, color matching method is an important technique, in whicha color reproducing region of the proof print produced by the proofpress is approximated to that of printed matter to be produced by aprinting press, thereby producing a visually similar result.

However, in many cases, the respective color reproducing regionsinherent to the printed matter and the proof print are different fromeach other, and thus, it is very difficult to accurately approximate thecolor reproducing regions to each other.

For example, black (Bk) ink is generally used in addition to threeprimary colors in a subtractive process, i.e., cyan (C), magenta (M) andyellow (Y) in a printing process. The use of the Bk ink produces aneconomic effect such as ink saving by expressing an Indian ink charactermainly used on a printing paper with monochromatic color ink as well asa quality improvement effect owing to an increase in density region in ahigh density part or color reproducing region.

There are two methods for making the black Bk from the three colors C, Mand Y: a full-black method and a skeleton black method.

Assuming that the colors C, M and Y are uniformly mixed into the blackBk, a value min(CMY), i.e., a minimum value out of values of the colorsC, M and Y is replaced with the black Bk, thereby achievingrepresentation with the three colors. This is a method for maximizing avalue replaced with the black Bk, and is referred to as the full blackmethod. In an example illustrated in FIG. 5, out of the values of thethree colors, i.e., C being 72%, M being 94% and Y being 43%, theminimum value Y is replaced with the black Bk, and further, issubtracted from the values of C and M. In this case, the amount equal to43%×2 of ink is saved.

In the full-black method, scum of the black Bk ink occurs at a highlightpart, which, therefore, looks dirt. Thus, as illustrated in FIG. 6, thevalue min(CMY) is not wholly replaced with the black Bk, but partlyremains. This method is referred to as the skeleton black method.

The ink colors C, M, Y and Bk are relative to each other. The ink colorsC, M, Y and Bk of printed matter produced by a printing press aredifferent from those of proof print produced by a color printing press.Moreover, even the ink colors C, M, Y and Bk of one and the same printedmatter slightly look different according to manufacturers. In view ofthis, the colors cannot be simply compared with each other as they are.Additionally, in comparison of the colors between a monitor and a colorprinting press, three colors R, G and B are used in the monitor, andtherefore, respective color spaces in the monitor and the color printingpress are different from each other.

Therefore, there has been conceived a method for, on the presumption ofan absolute color space independent of color representing means,replacing color represented objects in the absolute color space so as tocompare them with each other. This is referred to as a deviceindependent color.

The absolute color space originally signifies an xyz space which isobtained by numerating a stimulus value with respect to human eyes.Since this space is a markedly distorted space, it is not suitable forperceiving a color difference. Therefore, there has been proposed aspace rearranged in a uniformly three-dimensional space (a uniform colorspace). Currently, an Lab space is mainly used as the uniform colorspace. Since the uniform color space is the Euclidean space, the colordifference is readily obtained.

In actual color management, all of the color of the printed matter bythe printing press, and the color of the proof print by the colorprinting press and the color of the monitor are measured by aspectrophotometer, and then, their color reproducing regions arerepresented with the Lab values. Here, the colors can be simply comparedwith each other because of the same color space. Consequently, one ofthe color reproducing regions is compressed to the other, therebyachieving color matching. This is referred to as Gamut Mapping.

Here, since the color space after the color matching is the Lab space,the Lab space is converted again into respective relative color spaces,thereby obtaining actual conversion values. FIG. 7 illustrates anexample in which the above-described procedures are applied to the colormatching between the printed matter and the proof print.

In this manner, the device independent color is a remarkably effectivecolor management technique. However, there arises a serious problem inview of representation of the black color. That is, since the black is acolor which is artificially created, the original value of the black Bkis lost when the colors C, M, Y and Bk are converted to the colors inthe Lab space, which are further converted again to the colors C, M, Yand Bk. Namely, in this case, there exists no reversibility between thecolors C, M, Y and Bk before and after the conversion.

The most adverse effect on the actual processing is that a part havingan area factor of 100% of the black mainly used in the representation ofan Indian ink character or the like (C=M=Y=0, Bk=100) is lost, resultingin three or four colors (for example, C=71, M=75, Y=85 and Bk=35). Inother words, the Indian ink character cannot be sharply represented, andfurther, the ink need be used in a greater quantity.

Moreover, in the printing process, in the case where color proof ofoffset lithography or gravure printing is performed by the use of acolor printing press, a paper which can be used in the color printingpress for performing the proofing is different from a paper which can beused in a printing press for performing main printing (hereinafterreferred to as “a printing paper”) in most cases. In particular, specialpapers need be used in an ink jet printing press, a sublimation thermalink-transfer type printing press or the like, and therefore, the samepaper as the printing paper cannot be used in fact.

If printing papers are different, it is more difficult to approximatethe proof print to the printed matter.

In view of this, there has been conventionally a method for reproducingthe color of the printing paper on image data so as to visuallyapproximate the proof print to the printing paper. In this method, it ispossible to reproduce the printing paper in proofing with relative easeunless a paper special to the color printing press has so extreme acolor as to prevent reproducibility of the color of the printing paper,thereby obtaining the proof print which can be more approximated to theprinted matter.

However, in this method, there arises a problem not in a region on theproof print, to which no ink is transferred, i.e., a blank region, butin a region to which the ink is transferred, as follows: if the color ofthe paper is added to only the blank region to which no ink istransferred, the color of the paper is not added to the region to whichthe ink is transferred, and therefore, the original color remains as itis.

Since printing gradation representation is principally area gradation,the color of the ink and the color of the paper basically looks mixed ina visual way. In other words, the color of the paper visually has aneffect on the color of the ink. This effect is particularly shown moreat a highlight part having a low ink area factor, so that the effect ofthe color of the paper visually becomes greater.

Another method for approximating the proof print to the printed matterin the case where the printing papers are different is a method foruniformly adding the color of the paper to the entire printing image.This method is further classified into a method for adding the color ofthe printing paper to image data and a method for printing a printingimage after previous printing of the color of the printing paper overthe entire special paper. In the above-described methods, the colormatching between the proof print and the printed matter becomesexcellent at the highlight part with relative accuracy, but the exposurearea of the color of the paper is small from an intermediate part to ashadow part, and the color of the paper largely has an effect even on aregion which hardly gets an effect by the color of the paper, whereby acolor reproducing region of the proof print is markedly deviated from acolor reproducing region of the printed matter.

Thus, a problem to be solved by the present invention is to improve thecolor reproducibility of the printed matter by means of the printingpress in proofing by the proof press, in particular, by the colorprinting press.

Moreover, another problem to be solved by the present invention is toreproduce the color of the printing paper by means of the printingpress, so as to reproduce the representing characteristics of the blackink on the printed matter.

DISCLOSURE OF THE INVENTION

In order to solve the above-described problems, according to the presentinvention, there is provided a color proofing method for improving thecolor reproducibility of printed matter to be produced by a printingpress in proof print produced by a proof press, the color proofingmethod comprising the steps of: creating a look-up table containingconverted values of image data over the entire color space with respectto the proof press; correcting the look-up table based on the color ofprinting paper for the printing press and a paper exposed area factor inthe proof print; making proof print by the use of the corrected look-uptable; in the case where the proof print is produced based on areagradation and the colors of the printing paper for the printing pressand a printing paper for the proof press are approximated to each otherto such an extent as not to need to take the ink transmittance intoaccount, the step of correcting the look-up table includes the steps of:determining a paper exposed area factor α in accordance with thefollowing equation when arbitrary reference data P in the look-up tablehas color values (Cp, Mp, Yp, Bkp), each of which is N-bit data:α=(1−Cp/(2^(N)−1))×(1−Mp/(2^(N)−1)×(1−Yp/(2^(N)−1)×(1−Bkp/(2^(N)−1)),in contrast, determining the paper exposed area factor α in accordancewith the following equation when the arbitrary reference data P in thelook-up table has the color values (Cp, Mp, Yp, Bkp), each of which ispercentage data:α=(1Cp/100)×(1−Mp/100)×(1−Yp/100)×(1−Bkp/100);and determining corrected values (Ci′, Mi′, Yi′, Bki′) of color values(Ci, Mi, Yi, Bki) of arbitrary reference data I in the look-up table inaccordance with the following equations when color values (Ca, Ma, Ya,Bka) of the printing paper for the printing press are added to a partwhere a paper exposed area factor is 100%:Ci′=Ci+Ca×α, Mi′=Mi+Ma×α, Yi′=Yi+Ya×α and Bki′=Bki+Bka×α,to thus replace the color values of the reference data with thecorrected values.

Furthermore, in order to solve the above-described problems, accordingto the present invention, there is provided a color proofing method forimproving the color reproducibility of printed matter to be produced bya printing press in proof print produced by a proof press, the colorproofing method comprising the steps of: creating a look-up tablecontaining converted values of image data over the entire color spacewith respect to the proof press; correcting the look-up table based onthe color of printing paper for the printing press and a paper exposedarea factor in the proof print; making proof print by the use of thecorrected look-up table; in the case where the proof print is producedbased on both of density gradation and area gradation and the colors ofthe printing paper for the printing press and a printing paper for theproof press are approximated to each other to such an extent as not toneed to take the ink transmittance into account, the step of correctingthe look-up table includes the steps of: specifying an influence rangedefining how far reference data is influenced in the color space whenthe color values of the printing paper for the printing press are addedto the color space; and determining an influence value for each of thereference data based on the color values of the paper and the value ofthe influence range, to thus add the influence value to the referencedata.

Moreover, in order to solve the above-described problems, according tothe present invention, there is provided a color proofing method forimproving the color reproducibility of printed matter to be produced bya printing press in proof print produced by a proof press, the colorproofing method comprising the steps of: creating a look-up tablecontaining converted values of image data over the entire color spacewith respect to the proof press; correcting the look-up table based onthe color of printing paper for the printing press and a paper exposedarea factor in the proof print; making proof print by the use of thecorrected look-up table; in the case where the colors of the printingpaper for the printing press and a printing paper for the proof pressare different from each other to such an extent as to need to take theink transmittance into account, the step of correcting the look-up tableincludes the step of: determining corrected values (Ci′, Mi′, Yi′, Bki′)of color values (Ci, Mi, Yi, Bki) of arbitrary reference data I in thelook-up table in accordance with the following equations when colorvalues (Ca, Ma, Ya, Bka) of the printing paper for the printing pressare added to a part where a paper exposed area factor is 100%, whereinaddress values (Cid, Mid, Yid, Bkid) express the color values (Ci, Mi,Yi, Bki) by N-bit:Ci′=Ci+Ca×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));Mi′=Mi+Ma×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)) Bkid/(2^(N)−1)Yi′=Yi+Ya×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));andBki′=Bki+Bka×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));to thus replace the color values of the reference data with thecorrected values.

According to a preferred embodiment of the above-mentioned first tothird inventions, the step of creating the proof print includes the stepof: changing image data converted by using the corrected look-up tablebased on the previously determined noise strength and distributionamount indicating the level of a variation of the color of the printingpaper for the printing press, to thus make the proof print by the use ofthe changed image data.

Furthermore, in order to solve the above-described problems, accordingto the present invention, there is provided a color proofing method forimproving the color reproducibility of printed matter to be produced bya printing press in proof print produced by a proof press, the colorproofing method comprising the step of: correcting proof printing imagedata, in which each of levels of monochromatic color gradation of blackon the printed matter is represented on the proof print, out of theproof printing image data over the entire color space in a subtractiveprocess resulting from color matching between proof print produced bythe proof press and the printed matter to be produced by the printingpress in such a manner that a part having a black ink area factor of100% on the printed matter is represented only with black ink also onthe proof print, but that a part other than the part having a black inkarea factor of 100% on the printed matter is represented on the proofprint by using under color removal, to thus reproduce, on the proofprint, the representing characteristics of the black ink on the printedmatter.

According to a preferred embodiment of the above-mentioned fourthinvention, the step of correcting the proof printing image data includesthe steps of: finding min(C₁₀₀, M₁₀₀, Y₁₀₀) from color values (C₁₀₀,M₁₀₀, Y₁₀₀, Bk₁₀₀) of the proof printing image data for representing, onthe proof print, the part having the black ink area factor of 100% onthe printed matter, to thus determine a new value P of Bk₁₀₀; finding anaddition value α₁₀₀ for Bk₁₀₀ in accordance with the following equation:α=min (C ₁₀₀ , M ₁₀₀ , Y ₁₀₀)×(P−Bk ₁₀₀)/min (C ₁₀₀ , M ₁₀₀ , Y ₁₀₀),wherein 1≦P≦100;adding the addition value α₁₀₀ to Bk₁₀₀ as well as setting all of C₁₀₀,M₁₀₀ and Y₁₀₀ to 0; and repeating, with respect to n from 99 to 1, thefollowing steps of: determining min(C_(n), M_(n), Y_(n)) from colorvalues (C_(n), M_(n), Y_(n), Bk_(n)) of the proof printing image datafor representing, on the proof print, a part having a black ink areafactor of n% on the printed matter; determining an addition value α_(n)with respect to Bk_(n) in accordance with the following equation:α_(n)=(min(C _(n) , M _(n) , Y _(n))×(100−n))×(P−Bk ₁₀₀)/min(C ₁₀₀ , M₁₀₀ , Y ₁₀₀),wherein 1≦P≦100, to thus add the addition value α_(n) to Bk_(n); andobtaining respective reduction values β_(n), γ_(n) and δ_(n) of C_(n),M_(n) and Y_(n) in accordance with the following equations:β_(n)=α_(n)×((P−Bk ₁₀₀)/C ₁₀₀),γ_(n)=α_(n)×((P−Bk ₁₀₀)/M ₁₀₀), andδ_(n)=α_(n)×((P−Bk ₁₀₀)/Y ₁₀₀)wherein 1≦P≦100, to thus subtract the reduction values β_(n), γ_(n) andδ_(n)of C_(n), M_(n) and Y_(n), respectively.

Additionally, in order to solve the above-described problems, accordingto the present invention, there is provided a color proofing apparatusfor improving the color reproducibility of printed matter to be producedby a printing press in proof print produced by a proof press by the useof a computer, the color proofing apparatus comprising: a look-up tablecreating section for creating a look-up table including converted valuesof image data over the entire color space with respect to the proofpress; a noise strength and distribution amount input section forsetting the noise strength and distribution amount indicating the levelof a variation of the color of the printing paper for the printingpress; a paper color input section for specifying the color of theprinting paper for the printing press; a look-up table correctingsection for correcting the look-up table based on the color inputted tothe paper color input section and a paper exposed area factor in theproof print; an image data converting section for changing the imagedata converted by the use of the look-up table corrected by the look-uptable correcting section based on the noise strength and distributionamount inputted to the noise strength and distribution amount inputsection, to thus output the changed image data; in the case where theproof print is produced based on only area gradation and the colors ofthe printing paper for the printing press and a printing paper for theproof press are approximated to each other to such an extent as not toneed to take the ink transmittance into account, the look-up tablecorrecting section includes: a paper exposed area factor calculatingsection for determining a paper exposed area factor α in accordance withthe following equation when arbitrary reference data P in the look-uptable has color values (Cp, Mp, Yp, Bkp), each of which is N-bit data:α=(1−Cp/(2^(N)−1))×(1−Mp/(2^(N)−1,))×(1−Yp/(2^(N)−1))×(1−Bkp/(2^(N)−1)),in contrast, determining the paper exposed area factor α in accordancewith the following equation when the arbitrary reference data P in thelook-up table has the color values (Cp, Mp, Yp, Bkp), each of which ispercentage data:α=(1−Cp/100)×(1−Mp/100)×(1−Yp/100)×(1−Bkp/100);and a color corrected value calculating section for determiningcorrected values (Ci′, Mi′, Yi′, Bki′) of color values (Ci, Mi, Yi, Bki)of arbitrary reference data I in the look-up table in accordance withthe following equations when color values (Ca, Ma, Ya, Bka) of theprinting paper for the printing press are added to a part where a paperexposed area factor is 100%:Ci′=Ci+Ca×α, Mi′=Mi+Ma×α, Yi′=Yi+Ya×α and Bki′=Bki+Bka×α,to thus replace the color values of the reference data with thecorrected values.

Furthermore, in order to solve the above-described problems, accordingto the present invention, there is provided a color proofing apparatusfor improving the color reproducibility of printed matter to be producedby a printing press in proof print produced by a proof press by the useof a computer, the color proofing apparatus comprising: a look-up tablecreating section for creating a look-up table including converted valuesof image data over the entire color space with respect to the proofpress; a noise strength and distribution amount input section forsetting the noise strength and distribution amount indicating the levelof a variation of the color of the printing paper for the printingpress; a paper color input section for specifying the color of theprinting paper for the printing press; a look-up table correctingsection for correcting the look-up table based on the color inputted tothe paper color input section and a paper exposed area factor in theproof print and an image data converting section for changing the imagedata converted by the use of the look-up table corrected by the look-uptable correcting section based on the noise strength and distributionamount inputted to the noise strength and distribution amount inputsection, to thus output the changed image data; in the case where theproof print is produced based on both of density gradation and areagradation and the colors of the printing paper for the printing pressand a printing paper for the proof press are approximated to each otherto such an extent as not to need to take the ink transmittance intoaccount, the look-up table correcting section includes: an influencerange input section for specifying an influence range defining how farreference data is influenced in the color space when the color values ofthe printing paper for the printing press are added to the color space;and an influence value calculating section for determining an influencevalue for each of the reference data based on the color values of thepaper and the value of the influence range, to thus add the influencevalue to the reference data.

Furthermore, in order to solve the above-described problems, accordingto the present invention, there is provided a color proofing apparatusfor improving the color reproducibility of printed matter to be producedby a printing press in proof print produced by a proof press by the useof a computer, the color proofing apparatus comprising: a look-up tablecreating section for creating a look-up table including converted valuesof image data over the entire color space with respect to the proofpress; a noise strength and distribution amount input section forsetting the noise strength and distribution amount indicating the levelof a variation of the color of the printing paper for the printingpress; a paper color input section for specifying the color of theprinting paper for the printing press; a look-up table correctingsection for correcting the look-up table based on the color inputted tothe paper color input section and a paper exposed area factor in theproof print and an image data converting section for changing the imagedata converted by the use of the look-up table corrected by the look-uptable correcting section based on the noise strength and distributionamount inputted to the noise strength and distribution amount inputsection, to thus output the changed image data; in the case where thecolors of the printing paper for the printing press and a printing paperfor the proof press are different from each other to such an extent asto need to take the ink transmittance into account, the look up tablecorrecting section includes: a second color corrected value calculatingsection for determining corrected values (Ci′, Mi′, Yi′, Bki′) of colorvalues (Ci, Mi, Yi, Bki) of arbitrary reference data I in the look-uptable in accordance with the following equations when color values (Ca,Ma, Ya, Bka) of the printing paper for the printing press are added to apart where a paper exposed area factor is 100%, wherein address values(Cid, Mid, Yid, Bkid) express the color values (Ci, Mi, Yi, Bki) byN-bit:Ci′=Ci+Ca×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));Mi′=Mi+Ma×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));Yi′=Yi+Ya×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));andBki′=Bki+Bka×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));to thus replace the color values of the reference data with thecorrected values.

Furthermore, in order to solve the above-described problems, accordingto the present invention, there is provided a color proofing apparatusfor improving the color reproducibility of printed matter to be producedby a printing press in proof print produced by a proof press by the useof a computer, the color proofing apparatus comprising: an image datainput section for receiving an input of proof printing image data overthe entire color space in a subtractive process resulting from colormatching between proof print produced by the proof press and the printedmatter produced by the printing press; and an image data correctingsection for correcting the proof printing image data, in which each oflevels of monochromatic color gradation of black on the printed matteris represented on the proof print, out of the image data inputted to theimage data input section in such a manner that a part having a black inkarea factor of 100% on the printed matter is represented only with blackink also on the proof print, but that a part other than the part havinga black ink area factor of 100% on the printed matter is represented onthe proof print by using under color removal, to thus output thecorrected image data.

According to a preferred embodiment of the above-mentioned eighthinvention, the image data correcting section includes: a 100% black partimage data correcting section for determining min (C₁₀₀, N₁₀₀, Y₁₀₀)from color values (C₁₀₀, M₁₀₀, Y₁₀₀, Bk₁₀₀) of the proof printing imagedata for representing, on the proof print, the part having the black inkarea factor of 100% on the printed matter, to thus determine a new valueP of Bk₁₀₀, determining an addition value α₁₀₀ for Bk₁₀₀ in accordancewith the following equation:α₁₀₀=min(C ₁₀₀ , M ₁₀₀ , Y ₁₀₀)×(P−Bk ₁₀₀)/min(C ₁₀₀ , M ₁₀₀ , Y ₁₀₀),wherein 1≦P≦100and then, adding the addition value α₁₀₀ to Bk₁₀₀ as wellas setting all of C₁₀₀, M₁₀₀ and Y₁₀₀ to 0; and a 99% or less black partimage data correcting section for repeating, with respect to n from 99to 1, the following processes of: determining min(C_(n), M_(n), Y_(n))from color values (C_(n), M_(n), Y_(n), Bk_(n)) of the proof printingimage data for representing, on the proof print, a part having a blackink area factor of n% on the printed matter; determining an additionvalue α_(n) for Bk_(n) in accordance with the following equation:α_(n)=(min(C _(n) , M _(n) , Y _(n))−(100−n))×(P−Bk ₁₀₀)/min(C ₁₀₀ , M₁₀₀ , Y ₁₀₀),wherein 1≦P≦100, to thus add the addition value α_(n) to Bk_(n); anddetermining respective reduction values β_(n), γ_(n), and δ_(n), ofC_(n), M_(n), and Y_(n), in accordance with the following equations:β=α_(n)×((P−Bk ₁₀₀)/C ₁₀₀),γ=α_(n)×((P−Bk ₁₀₀)/M ₁₀₀), andδ=α_(n)×((P−Bk ₁₀₀)/Y ₁₀₀),wherein 1≦P≦100, to thus subtract the reduction values β_(n), γ_(n) andδ_(n) from C_(n), M_(n) and Y_(n), respectively.

Furthermore, in order to solve the above-described problems, accordingto the present invention, there is provided a recorded medium recordingtherein a color proofing program for improving the color reproducibilityof printed matter to be produced by a printing press in proof printproduced by a proof press by the use of a computer, the color proofingprogram instructing the computer to execute the processes of: creating alook-up table containing converted values of image data over the entirecolor space with respect to the proof press; correcting the look-uptable based on the color of printing paper for the printing press and apaper exposed area factor in the proof print; creating proof print bythe use of the corrected look-up table; in the case where the proofprint is produced based on only area gradation and the colors of theprinting paper for the printing press and a printing paper for the proofpress are approximated to each other to such an extent as not to need totake the ink transmittance into account, the look-up table correctingprocess includes the processes of: determining a paper exposed areafactor α in accordance with the following equation when arbitraryreference data P in the look-up table has color values (Cp, Mp, Yp,Bkp), each of which is N-bit data:α=(1−Cp/(2^(N)−1))×(1−Mp/(2^(N)−1))×(1−Yp/(2^(N)−1))×(1−Bkp/(2^(N)−1)),in contrast, determining the paper exposed area factor α in accordancewith the following equation when the arbitrary reference data P in thelook-up table has the color values (Cp, Mp, Yp, Bkp), each of which ispercentage data:α=(1−Cp/100)×(1−Mp/100)×(1−Yp/100)×(1−Bkp/100);and determining corrected values (Ci′, Mi′, Yi′, Bki′) of color values(Ci, Mi, Yi, Bki) of arbitrary reference data I in the look-up table inaccordance with the following equations when color values (Ca, Ma, Ya,Bka) of the printing paper for the printing press are added to a partwhere a paper exposed area factor is 100%:Ci′=Ci+Ca×α, Mi′=Mi+Ma×α, Yi′=Yi+Ya×α and Bki′=Bki+Bka×α,to thus replace the color values of the reference data with thecorrected values.

In addition, in order to solve the above-described problems, accordingto the present invention, there is provided a recorded medium recordingtherein a color proofing program for improving the color reproducibilityof printed matter to be produced by a printing press in proof printproduced by a proof press by the use of a computer, the color proofingprogram instructing the computer to execute the processes of: creating alook-up table containing converted values of image data over the entirecolor space with respect to the proof press; correcting the look-uptable based on the color of printing paper for the printing press and apaper exposed area factor in the proof print; creating proof print bythe use of the corrected look-up table; in the case where the proofprint is produced based on both of density gradation and area gradationand the colors of the printing paper for the printing press and aprinting paper for the proof press are approximated to each other tosuch an extent as not to need to take the ink transmittance intoaccount, the look-up table correcting process includes the processes of:specifying an influence range defining how far reference data isinfluenced in the color space when the color values of the printingpaper for the printing press are added to the color space; anddetermining an influence value for each of the reference data based onthe color values of the paper and the value of the influence range, tothus add the influence value to the reference data.

Moreover, in order to solve the above-described problems, according tothe present invention, there is provided a recorded medium recordingtherein a color proofing program for improving the color reproducibilityof printed matter to be produced by a printing press in proof printproduced by a proof press by the use of a computer, the color proofingprogram instructing the computer to execute the processes of: creating alook-up table containing converted values of image data over the entirecolor space with respect to the proof press; correcting the look-uptable based on the color of printing paper for the printing press and apaper exposed area factor in the proof print; creating proof print bythe use of the corrected look-up table; in the case where the colors ofthe printing paper for the printing press and a printing paper for theproof press are different from each other to such an extent as to needto take the ink transmittance into account, the look-up table correctingprocess includes the processes of: determining corrected values (Ci′,Mi′, Yi′, Bki′) of color values (Ci, Mi, Yi, Bki) of arbitrary referencedata I in the look-up table in accordance with the following equationswhen color values (Ca, Ma, Ya, Bka) of the printing paper for theprinting press are added to a part where a paper exposed area factor is100%, wherein address values (Cid, Mid, Yid, Bkid) express the colorvalues (Ci, Mi, Yi, Bki) by N-bit:Ci′=Ci+Ca×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));Mi′=Mi+Ma×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));Yi′=Yi+Ya×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));andBki′=Bki+Bka×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));to thus replace the color values of the reference data with thecorrected values.

According to a preferred embodiment of the above-mentioned ninth toeleventh invention, the proof print creating process includes theprocess of: changing image data converted by using the corrected look-uptable based on the previously determined noise strength and distributionamount indicating the level of a variation of the color of the printingpaper for the printing press, to thus create the proof print by the useof the changed image data.

Furthermore, in order to solve the above-described problems, accordingto the present invention, there is provided a recording medium recordingtherein the color proofing program for improving the colorreproducibility of printed matter to be produced by a printing press inproof print produced by a proof press by the use of a computer, thecolor proofing program further instructing the computer to execute theprocess of: correcting proof printing image data, in which each oflevels of monochromatic color gradation of black on the printed matteris represented on the proof print, out of the proof printing image dataover the entire color space in a subtractive process resulting fromcolor matching between proof print by the proof press and the printedmatter by means of the printing press in such a manner that a parthaving a black ink area factor of 100% on the printed matter isrepresented only with black ink also on the proof print, but that a partother than the part having a black ink area factor of 100% on theprinted matter is represented on the proof print by using under colorremoval, to thus reproduce, on the proof print, the representingcharacteristics of the black ink on the printed matter.

According to a preferred embodiment of the above-mentioned twelfthinvention, the proof printing image data correcting process includes theprocesses of: determining min(C₁₀₀, M₁₀₀, Y₁₀₀) from color values (C₁₀₀,M₁₀₀, Y₁₀₀, Bk₁₀₀) of the proof printing image data for representing, onthe proof print, the part having the black ink area factor of 100% onthe printed matter, to thus determine a new value P of Bk₁₀₀;determining an addition value α₁₀₀ for Bk₁₀₀ in accordance with thefollowing equation:α₁₀₀=min(C ₁₀₀ , M ₁₀₀ , Y ₁₀₀)×(P−Bk ₁₀₀)/min(C ₁₀₀ , M ₁₀₀ , Y ₁₀₀),wherein 1≦P≦100; adding the addition value α₁₀₀ to Bk₁₀₀ as well assetting all of C₁₀₀, M₁₀₀ and Y₁₀₀ to 0; and repeating, with respect ton from 99 to 1, the following steps of: determining min(C_(n), M_(n),Y_(n)) from color values (C_(n), M_(n), Y_(n), Bk_(n)) of the proofprinting image data for representing, on the proof print, a part havinga black ink area factor of n% on the printed matter; determining anaddition value α_(n) with respect to Bk_(n) in accordance with thefollowing equation:α_(n)=(min(C _(n) , M _(n) , Y _(n))−(100−n))×(P−Bk ₁₀₀)/min(C ₁₀₀ , M₁₀₀ , Y ₁₀₀),wherein 1≦P≦100, to thus add the addition value α_(n) to Bk_(n); anddetermining respective reduction values β_(n), γ_(n) and δ_(n), ofC_(n), M_(n), and Y_(n) in accordance with the following equations:β_(n)=α_(n)×((P−Bk ₁₀₀)/C ₁₀₀),γ_(n)=α_(n)×((P−Bk ₁₀₀)/M ₁₀₀), andδ_(n)=α_(n)×((P−Bk ₁₀₀)/Y ₁₀₀),wherein 1≦P≦100, to thus subtract the reduction values β_(n), γ_(n) andδ_(n), from C_(n), M_(n), and Y_(n), respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating the schematic configuration of acolor proofing method according to a preferred embodiment in the presentinvention;

FIG. 2 is a flowchart illustrating the schematic configuration of acolor proofing method according to another preferred embodiment in thepresent invention;

FIG. 3 is a block diagram illustrating the schematic configuration of acolor proofing apparatus according to a preferred embodiment in thepresent invention;

FIG. 4 is a block diagram illustrating the schematic configuration of acolor proofing apparatus according to another preferred embodiment inthe present invention;

FIG. 5 is a diagram illustrating a full black method;

FIG. 6 is a diagram illustrating a skeleton black method; and

FIG. 7 is a diagram illustrating a conventional method for performingcolor matching between printed matter and proof print.

BEST MODE CARRYING OUT THE INVENTION

A preferred embodiment of the present invention will be describedhereinafter with reference to the accompanying drawings. FIG. 1 is aflowchart illustrating the schematic configuration of a color proofingmethod according to a preferred embodiment of the present invention.Referring to FIG. 1, first, an luook-up table including corrected valuesof image data over the entire color space is created with respect to aproof press, for example, a color printing press (see Step (1) in FIG.1). Subsequently, the noise strength and distribution amount indicatingthe level of a variation of the color of a printing paper (a printingpaper) for the proof press is specified (see Step (2) in FIG. 1), andthen, the color of the printing paper is specified (see Step (3) in FIG.1).

Like in offset lithography, in the case where the proof print is createdin a printing system for performing only area gradation and the colorsof the printing paper and a printing paper for the proof press areapproximated to each other to such an extent as not to need to take theink transmittance into account, when arbitrary reference data P in thelook-up table has color values (Cp, Mp, Yp, Bkp), each of which is 8-bitdata, a paper exposed area factor a is determined in accordance with thefollowing equation:α=(1−Cp/255)×(1−Mp/255)×(1−Yp/255)×(1−Bkp/255)(see Step (4) in FIG. 1).

When the color values of the reference data are expressed by thepercentage, the paper exposed area factor a is determined in accordancewith the following equation:α=(1−Cp/100)×(1−Mp/100)×(1−Yp/100)×(1−Bkp/100).

Thereafter, corrected values (Ci′, Mi′, Yi′, Bki′) of color values (Ci,Mi, Yi, Bki) of arbitrary reference data I in the look-up table whencolor values (Ca, Ma, Ya, Bka) of the printing paper are added to a partwhere a paper exposed area factor is 100% are obtained in accordancewith the following equations:Ci′=Ci+Ca×α, Mi′=Mi+Ma×α, Yi′=Yi+Ya×α and Bki′=Bki+Bka×α

(see Step (5) in FIG. 1), to replace the color values of the referencedata with the corrected values (see Step (6) in FIG. 1), thus correctingthe look-up table (see Step (7) in FIG. 1).

Here, in the case of actually excellent printed matter, dot gaincharacteristics obtained by the Murray-Davies system or the Yule-Nielsensystem are represented by a curve which is expanded at a halftone partby about 10% to 20%. Consequently, similar curve characteristics aregiven with respect to a paper color effect rate, resulting in colorreproducibility approximate to the dot gain characteristics obtained bythe Murray-Davies system or the Yule-Nielsen system.

Like in gravure printing, in the case where the proof print is createdin a printing system for performing both of density gradation and areagradation and the colors of the printing paper and a printing paper forthe proof press are approximated to each other to such an extent as notto need to take the ink transmittance into account, an influence rangedefining how far reference data is influenced in the color space isspecified when the color values of the printing paper are added to thecolor space (see Step (8) in FIG. 1), an influence value for each of thereference data is obtained based on the color values of the paper andthe value of the influence range (see Step (9) in FIG. 1). The influencevalue is added to the reference data, thus correcting the look-up table(see Step (7) in FIG. 1).

Now, explanation will be made on a method for deriving the influencerange and the influence value. It is assumed that the color value (Ca,Ma, Ya, Bka) of the printing paper has linear or curve characteristicsover the entire color space or within a predetermined influence range,and has an effect on each of the reference data in the look-up table.Here, an influence value (Cieff, Mieff, Yieff, Bkieff) in the case wherethe color value (Ca, Ma, Ya, Bka) of the paper linearly has an effect onthe color value (Ci, Mi, Yi, Bki) of arbitrary reference data I isobtained as described below.

First, the paper color effect rate in the reference data I is set to beequal to a ratio of a distance from the coordinate (x=0, y=0, z=0, w=0)at a point Q where the paper color value over the entire color space isintroduced, to the coordinate of the reference data I. Assuming that thecoordinate of the reference data I is represented by (x_(i), y_(i),z_(i), w_(i)), the distance D between the point Q and the reference dataI is defined in accordance with the following equation:D=max(|x _(i)−0|, |y _(i)−0|, |z _(i)−0|, |w _(i)−0|)wherein, max(a, b, c) signifies a maximum value taken out of a, b and c.

The influence values with respect to the reference value I are expressedas follows:Cieff=Ca×(255×D)/255Mieff=Ma×(255×D)/255Yieff=Ya×(255×D)/255Bkieff=Bka×(255×D)/255Here, each of the values is 8-bit data. Incidentally, when each of thevalues is expressed in the percentage, the influence values with respectto the reference value I are expressed as follows:Cieff=Ca×(100×D)/100Mieff=Ma×(100×D)/100Yieff=Ya×(100×D)/100Bkieff=Bka×(100×D)/100

In the case where the colors of the printing paper and a printing paperfor the proof press are different from each other to such an extent asto need to take the ink transmittance into account, corrected values(Ci′, Mi′, Yi′, Bki′) of color values (Ci, Mi, Yi, Bki) of arbitraryreference data I in the look-up table when color values (Ca, Ma, Ya,Bka) of the printing paper are added to a part where a paper exposedarea factor is 100%, wherein address values (Cid, Mid, Yid, Bkid)express the color values (Ci, Mi, Yi, Bki) by N-bit are determined inaccordance with the following equations:Ci′=Ci+Ca×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));Mi′=Mi+Ma×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));Yi′=Yi+Ya×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));andBki′=Bki+Bka×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));to thus replace the color values of the reference data with thecorrected values (see Step (10) in FIG. 1).

Image data converted by using the look-up table corrected in theabove-described manner is changed based on the noise strength anddistribution amount (see Step (11) in FIG. 1). The proof print iscreated based on the changed image data by the color printing press (seeStep (12) in FIG. 1)

Also in this case, although no optical dot gain value is taken intoconsideration when the paper color effect rate is linearly taken, theobject can be sufficiently achieved by deriving an effect rate addedwith appropriate curve characteristics.

The color of the printing paper can be reproduced on the formed proofprint with accuracy.

FIG. 2 is a flowchart illustrating the schematic configuration of acolor proofing method according to another preferred embodiment in thepresent invention. Referring to FIG. 2, first, proof printing imagedata, in which each of levels of monochromatic color gradation of blackon printed matter is represented on proof print, is extracted out of theproof printing image data over the entire color space in a subtractiveprocess resulting from color matching between the proof print by theproof press and the printed matter by means of the printing press (seeStep (20) in FIG. 2).

And then, min(C₁₀₀, M₁₀₀, Y₁₀₀) is obtained from color values (C₁₀₀,M₁₀₀, Y₁₀₀, Bk₁₀₀) of the proof printing image data for representing, onthe proof print, the part having the black ink area factor of 100% onthe printed matter (see Step (21) in FIG. 2), and then, a new value P ofBk₁₀₀ is determined (see Step (22) in FIG. 2). Thereafter, an additionvalue α₁₀₀ for Bk₁₀₀ is obtained in accordance with the followingequation:α₁₀₀=min(C ₁₀₀ , M ₁₀₀ , Y ₁₀₀)×(P−Bk ₁₀₀)/min(C ₁₀₀ , M ₁₀₀ , Y ₁₀₀),wherein 1≦P≦100 (see Step (23) in FIG. 2). Subsequently, the additionvalue α₁₀₀ is added to Bk₁₀₀, and further, all of C₁₀₀, M₁₀₀ and Y₁₀₀are set to 0 (see Step (24) in FIG. 2).

Furthermore, with respect to n from 99 to 1, processes (a) to (c)described below are repeated (see Steps (25) to (30) in FIG. 2).

(a) min(C_(n), M_(n), Y_(n)) is obtained from color values (C_(n),M_(n), Y_(n), Bk_(n)) of the proof printing image data for representing,on the proof print, a part having a black ink area factor of n% on theprinted matter (see Step (27) in FIG. 2);

(b) an addition value α_(n) for Bk_(n) is determined in accordance withthe following equation:α_(n)=(min(C _(n) , M _(n) , Y _(n))−(100−n))×(P−Bk ₁₀₀)/min(C ₁₀₀ , M₁₀₀ , Y ₁₀₀),wherein 1≦P≦100, to thus add the addition value α_(n) to Bk_(n) (seeStep (28) in FIG. 2); and

(c) respective reduction values β_(n), γ_(n) and δ_(n) of C_(n), M_(n),and Y_(n) are determined in accordance with the following equations:β_(n)=α_(n)×((P−Bk ₁₀₀)/C ₁₀₀),γ_(n)=α_(n)×((P−Bk ₁₀₀)/M ₁₀₀), andδ_(n)=α_(n)×((P−Bk ₁₀₀)/Y ₁₀₀),wherein 1≦P≦100, to thus subtract the reduction values β_(n), γ_(n) andδ_(n) from C_(n), M_(n) and Y_(n), respectively (see Step (29) in FIG.2).

The proofing is performed by the color printing press based on the proofprinting image data which is corrected in the above-described manner andin which each of levels of monochromatic color gradation of black on theprinted matter is represented on the proof print and the othernot-corrected proof printing image data (see Step (31) in FIG. 2).

On the obtained proof print is reproduced a part having an area factorof 100% of the black ink used much in representing an Indian inkcharacter or the like on the printed matter. In this manner, therepresenting characteristics of the black ink on the printed matter canbe reproduced with accuracy. Moreover, the black ink is used as much aspossible on the proof print, so that the use amount of ink C, M or Y canbe reduced, thereby saving the cost of the proofing.

If a color proofing program for instructing a computer to execute thecolor proofing method according to the present invention is recorded ina recording medium such as a flexible disk or a CD-ROM, the computerreads the recording medium, thereby readily carrying out the colorproofing method according to the present invention.

FIG. 3 is a block diagram illustrating the schematic configuration of acolor proofing apparatus according to a preferred embodiment in thepresent invention. The color proofing apparatus according to the presentinvention is adapted to improve the color reproducibility of printedmatter by a printing press in proofing by a proof press by the use of acomputer. As illustrated in FIG. 3, the color proofing apparatusaccording to the present invention comprises: a look-up table creatingsection 40 for creating a look-up table including converted values ofimage data over the entire color space with respect to the proof press;a noise strength and distribution amount input section 41 for settingthe noise strength and distribution amount indicating the level of avariation of the color of a printing paper for the printing press (aprinting paper); and a paper color input section 42 for specifying thecolor of the printing paper for the printing press. The color proofingapparatus further comprises: a look-up table correcting section 43 forcorrecting the look-up table based on the color inputted to the papercolor input section 42 and a paper exposed area factor in the proofprint; and an image data converting section 44 for changing the imagedata converted by the use of the look-up table corrected by the look-uptable correcting section 43 based on the noise strength and distributionamount inputted to the noise strength and distribution amount inputsection 41, to thus output the changed image data.

In the case where the proof print is produced in a printing system forperforming only area gradation and the colors of the printing paper anda printing paper for the proof press are approximated to each other tosuch an extent as not to need to take the ink transmittance intoaccount, the look-up table correcting section 43 includes a paperexposed area factor calculating section 45 for determining a paperexposed area factor a in accordance with the following equation, whenarbitrary reference data P in the look-up table has color values (Cp,Mp, Yp, Bkp), each of which is N-bit data:α=(1−Cp/(2^(N)−1))×(1−Mp/(2^(N)−1))×(1−Yp/(2^(N)−1))×(1−Bkp/(2^(N)−1)),in contrast, determining the paper exposed area factor α in accordancewith the following equation, when the arbitrary reference data P in thelook-up table has the color values (Cp, Mp, Yp, Bkp), each of which ispercentage data:α=(1−Cp/100)×(1−Mp/100)×(1−Yp/100)×(1−Bkp/100);and a color corrected value calculating section 46 for determiningcorrected values (Ci′, Mi′, Yi′, Bki′) of color values (Ci, Mi, Yi, Bki)of arbitrary reference data I in the look-up table in accordance withthe following equations when color values (Ca, Ma, Ya, Bka) of theprinting paper for the printing press are added to a part where a paperexposed area factor is 100%:Ci′=Ci+Ca×α, Mi′=Mi+Ma×α, Yi′=Yi+Ya×α and Bki′=Bki+Bka×α,to thus replace the color values of the reference data with thecorrected values.

In the case where the proof print is produced in a printing system forperforming both of density gradation and area gradation and the colorsof the printing paper and a printing paper for the proof press areapproximated to each other to such an extent as not to need to take theink transmittance into account, the look-up table correcting section 43includes an influence range input section 47 for specifying an influencerange defining how far reference data is influenced in the color spacewhen the color values of the printing paper are added to the colorspace; and an influence value calculating section 48 for determining aninfluence value for each of the reference data based on the color valuesof the paper and the value of the influence range, to thus add theinfluence value to the reference data.

In the case where the colors of the printing paper and a printing paperfor the proof press are different from each other to such an extent asto need to take the ink transmittance into account, the look-up tablecorrecting section 43 includes a second color corrected valuecalculating section 49 for determining corrected values (Ci′, Mi′, Yi′,Bki′) of color values (Ci, Mi, Yi, Bki) of arbitrary reference data I inthe look-up table in accordance with the following equations when colorvalues (Ca, Ma, Ya, Bka) of the printing paper for the printing pressare added to a part where a paper exposed area factor is 100%, whereinaddress values (Cid, Mid, Yid, Bkid) express the color values (Ci, Mi,Yi, Bki) by N-bit;Ci′Ci+Ca×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1))×Bkid/(2^(N)−1));Mi′=Mi+Ma×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));Yi′=Yi+Ya×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));andBki′=Bki+Bka×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));to thus replace the color values of the reference data with thecorrected values.

FIG. 4 is a block diagram illustrating the schematic configuration of acolor proofing apparatus according to another preferred embodiment ofthe present invention. The color proofing apparatus according to thepresent invention is adapted to improve the color reproducibility of aprinting paper in proofing by means of a proof press by the use of acomputer. As illustrated in FIG. 4, the color proofing apparatusaccording to the present invention comprises an image data input section50 for receiving an input of proof printing image data over the entirecolor space in a subtractive process resulting from color matchingbetween proof print produced by the proof press and the printed matterto be produced by the printing press; and an image data correctingsection 51 for correcting the proof printing image data, in which eachof levels of monochromatic color gradation of black on the printedmatter is represented on the proof print, out of the image data inputtedto the image data input section 50 in such a manner that a part having ablack ink area factor of 100% on the printed matter is represented onlywith black ink also on the proof print, but that a part other than thepart having a black ink area factor of 100% on the printed matter isrepresented on the proof print by using under color removal, to thusoutput the corrected image data.

The image data correcting section 51 includes a 100% black part imagedata correcting section 52 for determining min(C₁₀₀, M₁₀₀, Y₁₀₀) fromcolor values (C₁₀₀, M₁₀₀, Y₁₀₀, Bk₁₀₀) of the proof printing image datafor representing, on the proof print, the part having the black ink areafactor of 100% on the printed matter, to thus determine a new value P ofBk₁₀₀, determining an addition value α₁₀₀ for Bk₁₀₀ in accordance withthe following equation:α₁₀₀=min(C ₁₀₀ , M ₁₀₀ , Y ₁₀₀)×(P−Bk ₁₀₀)/min(C ₁₀₀ , M ₁₀₀ , Y ₁₀₀),wherein 1≦P≦100, and then, adding the addition value α₁₀₀ to Bk₁₀₀ aswell as setting all of C₁₀₀, M₁₀₀ and Y₁₀₀ to 0; and a 99% or less blackpart image data correcting section 53 for repeating, with respect to nfrom 99 to 1, the following processes of determining min(C_(n), M_(n),Y_(n)) from color values (C_(n), M_(n), Y_(n), Bk_(n)) of the proofprinting image data for representing, on the proof print, a part havinga black ink area factor of n% on the printed matter; determining anaddition value α_(n) for Bk_(n) in accordance with the followingequation:α_(n)=(min(C _(n) , M _(n) , Y _(n))−(100−n))×(P−Bk ₁₀₀)/min(C ₁₀₀ , M₁₀₀ , Y ₁₀₀),wherein 1≦P≦100, to thus add the addition value α_(n) to Bk_(n); anddetermining respective reduction values β_(n), γ_(n) and δ_(n) forC_(n), M_(n) and Y_(n) in accordance with the following equations:β_(n)=α_(n)×((P−Bk ₁₀₀)/C ₁₀₀),γ_(n)=α_(n)×((P−Bk ₁₀₀)/M ₁₀₀), andδ_(n)=α_(n)×((P−Bk ₁₀₀)/Y ₁₀₀),wherein 1≦P≦100, to thus subtract the reduction values β_(n), γ_(n) andδ_(n) from C_(n), M_(n) and Y_(n), respectively.

INDUSTRIAL UTILIZABILITY

As described above, according to the present invention, it is possibleto readily achieve the color reproducibility of the high accuracybetween the printed matter and the proof print in the color proofing. Inparticular, according to the present invention, it is possible toreproduce the representing characteristics of the color of the printedmatter and the black ink on the printed matter with the high accuracy inthe proofing. Thus, the present invention can remarkably contribute tothe efficiency of the proofing work.

The invention claimed is:
 1. A color proofing apparatus for improvingthe color reproducibility of printed matter to be produced by a printingpress in proof print produced by a proof press by the use of a computer,the color proofing apparatus comprising: a look-up table creatingsection for creating a look-up table including converted values of imagedata over the entire color space with respect to the proof press; anoise strength and distribution amount input section for setting thenoise strength and distribution amount indicating the level of avariation of the color of the printing paper for the printing press; apaper color input section for specifying the color of the printing paperfor the printing press; a look-up table correcting section forcorrecting the look-up table based on the color inputted to the papercolor input section and a paper exposed area factor in the proof print;an image data converting section for changing the image data convertedby the use of the look-up table corrected by the look-up tablecorrecting section based on the noise strength and distribution amountinputted to the noise strength and distribution amount input section, tothus output the changed image data; in the case where the proof print isproduced based on only area gradation and the colors of the printingpaper for the printing press and a printing paper for the proof pressare approximated to each other to such an extent as not to need to takethe ink transmittance into account, the look-up table correcting sectionincludes: a paper exposed area factor calculating section fordetermining a paper exposed area factor α in accordance with thefollowing equation when arbitrary reference data P in the look-up tablehas color values (Cp, Mp, Yp, Bkp), each of which is N-bit data:α=(1−Cp/(2^(N)−1))×(1−Mp/(2^(N)−1))×(1−Yp/(2^(N)−1))×(1−Bkp/(2^(N)−1)),in contrast, determining the paper exposed area factor α in accordancewith the following equation when the arbitrary reference data P in thelook-up table has the color values (Cp, Mp, Yp, Bkp), each of which ispercentage data:α=(1−Cp/100)×(1−Mp/100)×(1−Yp/100)×(1−Bkp/100); and a color correctedvalue calculating section for determining corrected values (Ci′, Mi′,Yi′, Bki′) of color values (Ci, Mi, Yi, Bki) of arbitrary reference dataI in the look-up table in accordance with the following equations whencolor values (Ca, Ma, Ya, Bka) of the printing paper for the printingpress are added to a part where a paper exposed area factor is 100%:Ci′=Ci+Ca×α, Mi′=Mi+Ma×α, Yi′=Yi+Ya×α and Bki′=Bki+Bka×α, to thusreplace the color values of the reference data with the correctedvalues.
 2. A color proofing method for improving the colorreproducibility of printed matter to be produced by a printing press inproof print produced by a proof press, the color proofing methodcomprising the steps of: creating a look-up table containing convertedvalues of image data over the entire color space with respect to theproof press; correcting the look-up table based on the color of printingpaper for the printing press and a paper exposed area factor in theproof print; making proof print by the use of the corrected look-uptable; in the case where the proof print is produced based on areagradation and the colors of the printing paper for the printing pressand a printing paper for the proof press are approximated to each otherto such an extent as not to need to take the ink transmittance intoaccount, the step of correcting the look-up table includes the steps of:determining a paper exposed area factor α in accordance with thefollowing equation when arbitrary reference data P in the look-up tablehas color values (Cp, Mp, Yp, Bkp), each of which is N-bit data:α=(1−Cp/(2^(N)−1))×(1−Mp/(2^(N)−1))×(1−Yp/(2^(N)−1))×(1−Bkp/(2^(N)−1)),in contrast, determining the paper exposed area factor α in accordancewith the following equation when the arbitrary reference data P in thelook-up table has the color values (Cp, Mp, Yp, Bkp), each of which ispercentage data:α=(1−Cp/100)×(1−Mp/100)×(1−Yp/100)×(1−Bkp/100); and determiningcorrected values (Ci′, Mi′, Yi′, Bki′) of color values (Ci, Mi, Yi, Bki)of arbitrary reference data I in the look-up table in accordance withthe following equations when color values (Ca, Ma, Ya, Bka) of theprinting paper for the printing press are added to a part where a paperexposed area factor is 100%:Ci′=Ci+Ca×α, Mi′=Mi+Ma×α, Yi′=Yi+Ya×α and Bki′=Bki+Bka×α, to thusreplace the color values of the reference data with the correctedvalues.
 3. The color proofing method according to claim 2, wherein thestep of creating the proof print includes the step of: changing imagedata converted by using the corrected look-up table based on thepreviously determined noise strength and distribution mount indicatingthe level of a variation of the color of the printing paper for theprinting press, to thus make the proof print by the use of the changedimage data.
 4. A color proofing method for improving the colorreproducibility of printed matter to be produced by a printing press inproof print produced by a proof press, the color proofing methodcomprising the steps of: creating a look-up table containing convertedvalues of image data over the entire color space with respect to theproof press; correcting the look-up table based on the color of printingpaper for the printing press and a paper exposed area factor in theproof print; making proof print by the use of the corrected look-uptable; in the case where the colors of the printing paper for theprinting press and a printing paper for the proof press are differentfrom each other to such an extent as to need to take the inktransmittance into account, the step of correcting the look-up tableincludes the step of: determining corrected values (Ci′, Mi′, Yi′, Bki′)of color values (Ci, Mi, Yi, Bki) of arbitrary reference data I in thelook-up table in accordance with the following equations when colorvalues (Ca, Ma, Ya, Bka) of the printing paper for the printing pressare added to a part where a paper exposed area factor is 100%, whereinaddress values (Cid, Mid, Yid, Bkid) express the color values (Ci, Mi,Yi, Bki) by N-bit:Ci′=Ci+Ca×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));Mi′=Mi+Ma×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));Yi′=Yi+Ya×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));andBki′=Bki+Bka×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));to thus replace the color values of the reference data with thecorrected values.
 5. The color proofing method according to claim 4,wherein the step of creating the proof print includes the step of:changing image data converted by using the corrected look-up table basedon the previously determined noise strength and distribution amountindicating the level of a variation of the color of the printing paperfor the printing press, to thus make the proof print by the use of thechanged image data.
 6. A color proofing method for improving the colorreproducibility of printed matter to be produced by a printing press inproof print produced by a proof press, the color proofing methodcomprising the steps of: creating a look-up table containing convertedvalues of image data over the entire color space with respect to theproof press; correcting the look-up table based on the color of printingpaper for the printing press and a paper exposed area factor in theproof print; making proof print by the use of the corrected look-uptable; in the case where the proof print is produced based on both ofdensity gradation and area gradation and the colors of the printingpaper for the printing press and a printing paper for the proof pressare approximated to each other to such an extent as not to need to takethe ink transmittance into account, the step of correcting the look-uptable includes the steps of: specifying an influence range defining howfar reference data is influenced in the color space when the colorvalues of the printing paper for the printing press are added to thecolor space; and determining an influence value for each of thereference data based on the color values of the paper and the value ofthe influence range, to thus add the influence value to the referencedata.
 7. The color proofing method according to claim 6, wherein thestep of creating the proof print includes the step of: changing imagedata converted by using the corrected look-up table based on thepreviously determined noise strength and distribution mount indicatingthe level of a variation of the color of the printing paper for theprinting press, to thus make the proof print by the use of the changedimage data.
 8. A computer readable medium recording therein a colorproofing program for improving the color reproducibility of printedmatter to be produced by a printing press in proof print produced by aproof press by the use of a computer, the color proofing programinstructing the computer to execute the processes of: creating a look-uptable containing converted values of image data over the entire colorspace with respect to the proof press; correcting the look-up tablebased on the color of printing paper for the printing press and a paperexposed area factor in the proof print; creating proof print by the useof the corrected look-up table; in the case where the proof print isproduced based on only area gradation and the colors of the printingpaper for the printing press and a printing paper for the proof pressare approximated to each other to such an extent as not to need to takethe ink transmittance into account, the look-up table correcting processincludes the processes of: determining a paper exposed area factor α inaccordance with the following equation when arbitrary reference data Pin the look-tip table has color values (Cp, Np, Yp, Bkp), each of whichis N-bit data:α=(1−Cp/(2^(N)−1))×(1−Mp/(2^(N)−1))×(1−Yp/(2^(N)−1))×(1−Bkp/(2^(N)−1)),in contrast, determining the paper exposed area factor α in accordancewith the following equation when the arbitrary reference data P in thelook-up table has the color values (Cp, Mp, Yp, Bkp), each of which ispercentage data:α=(1−Cp/100)×(1−Mp/100)×(1−Yp/100)×(1−Bkp/100); and determiningcorrected values (Ci′, Ni′, Yi′, Bki′) of color values (Ci, Ni, Yi, Bki)of arbitrary reference data I in the look-up table in accordance withthe following equations when color values (Ca, Ma, Ya, Bka) of theprinting paper for the printing press are added to a part where a paperexposed area factor is 100%:Ci′=Ci+Ca×α, Mi′=Mi+Ma×α, Yi′=Yi+Ya×α and Bki′=Bki+Bka×α, to thusreplace the color values of the reference data with the correctedvalues.
 9. The computer readable medium recording therein the colorproofing program according to claim 8, wherein the proof print creatingprocess includes the process of: changing image data converted by usingthe corrected look-up table based on the previously determined noisestrength and distribution amount indicating the level of a variation ofthe color of the printing paper for the printing press, to thus createthe proof print by the use of the changed image data.
 10. A colorproofing apparatus for improving the color reproducibility of printedmatter to be produced by a printing press in proof print produced by aproof press by the use of a computer, the color proofing apparatuscomprising: a look-up table creating section for creating a look-uptable including converted values of image data over the entire colorspace with respect to the proof press; a noise strength and distributionamount input section for setting the noise strength and distributionamount indicating the level of a variation of the color of the printingpaper for the printing press; a paper color input section for specifyingthe color of the printing paper for the printing press; a look-up tablecorrecting section for correcting the look-up table based on the colorinputted to the paper color input section and a paper exposed areafactor in the proof print and an image data converting section forchanging the image data converted by the use of the look-up tablecorrected by the look-up table correcting section based on the noisestrength and distribution amount inputted to the noise strength anddistribution amount input section, to thus output the changed image datain the case where the proof print is produced based on both of densitygradation and area gradation and the colors of the printing paper forthe printing press and a printing paper for the proof press areapproximated to each other to such an extent as not to need to take theink transmittance into account, the look-up table correcting sectionincludes: an influence range input section for specifying an influencerange defining how far reference data is influenced in the color spacewhen the color values of the printing paper for the printing press areadded to the color space; and an influence value calculating section fordetermining an influence value for each of the reference data based onthe color values of the paper and the value of the influence range, tothus add the influence value to the reference data.
 11. A color proofingapparatus for improving the color reproducibility of printed matter tobe produced by a printing press in proof print produced by a proof pressby the use of a computer, the color proofing apparatus comprising: alook-up table creating section for creating a look-up table includingconverted values of image data over the entire color space with respectto the proof press; a noise strength and distribution amount inputsection for setting the noise strength and distribution amountindicating the level of a variation of the color of the printing paperfor the printing press; a paper color input section for specifying thecolor of the printing paper for the printing press; a look-up tablecorrecting section for correcting the look-up table based on the colorinputted to the paper color input section and a paper exposed areafactor in the proof print and an image data converting section forchanging the image data converted by the use of the look-up tablecorrected by the look-up table correcting section based on the noisestrength and distribution amount inputted to the noise strength anddistribution amount input section, to thus output the changed imagedata; in the case where the colors of the printing paper for theprinting press and a printing paper for the proof press are differentfrom each other to such an extent as to need to take the inktransmittance into account, the look-up table correcting sectionincludes: a second color corrected value calculating section fordetermining corrected values (Ci′, Ni′, Yi′, Bki′) of color values (Ci,Mi, Yi, Bki) of arbitrary reference data I in the look-up table inaccordance with the following equations when color values (Ca, Ma, Ya,Bka) of the printing paper for the printing press are added to a partwhere a paper exposed area factor is 100%, wherein address values (Cid,Mid, Yid, Bkid) express the color values (Ci, Mi, Yi, Bki) by N-bit:Ci′=Ci+Ca×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));Mi′=Mi+Ma×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));Yi′=Yi+Ya×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2⁻¹)); andBki′=Bki+Bka×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));to thus replace the color values of the reference data with thecorrected values.
 12. A computer readable medium recording therein acolor proofing program for improving the color reproducibility ofprinted matter to be produced by a printing press in proof printproduced by a proof press by the use of a computer, the color proofingprogram instructing the computer to execute the processes of: creating alook-up table containing converted values of image data over the entirecolor space with respect to the proof press; correcting the look-uptable based on the color of printing paper for the printing press and apaper exposed area factor in the proof print: creating proof print bythe use of the corrected look-up table; in the case where the proofprint is produced based on both of density gradation and area gradationand the colors of the printing paper for the printing press and aprinting paper for the proof press are approximated to each other tosuch an extent as not to need to take the ink transmittance intoaccount, the look-up table correcting process includes the processes of:specifying an influence range defining how far reference data isinfluenced in the color space when the color values of the printingpaper for the printing press are added to the color space; anddetermining an influence value for each of the reference data based onthe color values of the paper and the value of the influence range, tothus add the influence value to the reference data.
 13. The computerreadable medium recording therein the color proofing program accordingto claim 12, wherein the proof print creating process includes theprocess of: changing image data converted by using the corrected look-uptable based on the previously determined noise strength and distributionamount indicating the level of a variation of the color of the printingpaper for the printing press, to thus create the proof print by the useof the changed image data.
 14. A computer readable medium recordingtherein a color proofing program for improving the color reproducibilityof printed matter to be produced by a printing press in proof printproduced by a proof press by the use of a computer, the color proofingprogram instructing the computer to execute the processes of: creating alook-up table containing converted values of image data over the entirecolor space with respect to the proof press; correcting the look-uptable based on the color of printing paper for the printing press and apaper exposed area factor in the proof print; creating proof print bythe use of the corrected look-up table; in the case where the colors ofthe printing paper for the printing press and a printing paper for theproof press are different from each other to such an extent as to needto take the ink transmittance into account, the look-up table correctingprocess includes the processes of: determining corrected values (Ci′,Mi′, Yi′, Bki′) of color values (Ci, Mi, Yi, Bki) of arbitrary referencedata I in the look-up table in accordance with the following equationswhen color values (Ca, Ma, Ya, Bka) of the printing paper for theprinting press are added to a part where a paper exposed area factor is100%, wherein address values (Cid, Mid, Yid, Bkid) express the colorvalues (Ci, Mi, Yi, Bki) by N-bit:Ci′=Ci+Ca×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));Mi′=Mi+Ma×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));Yi′=Yi+Ya×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));andBki′=Bki+Bka×(1−Cid/(2^(N)−1)×Mid/(2^(N)−1)×Yid/(2^(N)−1)×Bkid/(2^(N)−1));to thus replace the color values of the reference data with thecorrected values.
 15. A computer readable medium recording therein thecolor proofing program according to claim 14, wherein the proof printcreating process includes the process of: changing image data convertedby using the corrected look-up table based on the previously determinednoise strength and distribution amount indicating the level of avariation of the color of the printing paper for the printing press, tothus create the proof print by the use of the changed image data.